It is known to glue containers together to form cluster packs. The spots at which the glue joins containers are often called “glue joints.”
Containers frequently carry labels. The force holding the label to the container is often weaker than the force that would result from gluing directly to the container. Therefore it is preferable to form the glue joints so that the glue bonds directly to the container, and not to the label.
A difficulty that arises is that sometimes labels are quite large. Very often, they go all the way around the container. This means that many of the locations at which one might want to form the glue joints are covered by the label. Since the glue joints would then be formed on the label and not directly on the container, the bond will not be as strong.
The use of a large label therefore makes it difficult to join containers with glue because the label eaves fewer places available to form glued joints of adequate strength.